This invention relates to the construction of improved X-ray intensifying screens useful for medical radiography, said screens having the effect of reducing the graininess due to quantum mottle in the images reproduced on silver halide film and thereby improving image quality. The quantum mottle has the effect of obscuring fine details in the images of the object exposed to medical radiography by the nature of the statistical process of absorption of X-rays in the intensifying screen. The resulting image has a non-uniform darkening which is observed as a film graininess on the order of about 0.01 mm.sup.2 size variations noticeable to the eye.
The present invention reduces this problem of quantum mottle by means of screens with two or more contiguous phosphor layer constructed in such a manner that the layers are of increasing luminous efficiency under X-ray excitation from the phosphor layer nearest the film to the outermost phosphor layer from said film which is customarily disposed nearest a reflector layer.
In contrast, the prior art screens are constructed of a single homogeneous phosphor layer of uniform brightness and consequently the greater degree of quantum mottle is caused primarily by the exposure of the film to bright emission of particles nearest the film and thus fewer absorbed X-ray photons are needed in the process leading to greater quantum mottle.